1. Field of the Invention
The present invention relates to a cyclic thermal solvent single well stimulation method utilizing hot visbroken produced oil as the solvent injected into the oil formation in order to reduce the viscosity of the oil in the formation and thereby enhance recovery of the oil from the formation.
2. Background of the Invention
Current primary oil production practices fail to recover much of the oil originally in place in natural formations. As a consequence thereof, much effort has been devoted to devising so-called secondary recovery methods of improving the ultimate recovert of the oil in the formations.
Various methods for inducing the recovery of viscous oil from underground formations are in existence. One such method is miscible flooding wherein a solvent for the oil is introduced into the formation and driven through the formation to displace the oil toward a production well from which oil is recovered. The solvents employed in these processes are expensive and the cost of solvent flooding is usually excessive in relation to the oil production obtainable thereby.
In U.S. Pat. No. 3,080,918 to Natland there is disclosed a process for heating produced oil by means of a nuclear reactor and passing the heated oil into the oil formation to reduce the viscosity of the oil and stimulate its recovery. The nuclear reactor is positioned in the well through which the produced oil is injected into the formation.
U.S. Pat. No. 4,174,752 to Slater et al discloses a method for heating recovered crude oil by solar means at the site of recovery thereof and injecting at least a portion of such heated crude oil back into the oil formation in order to reduce the viscosity of oil remaining in the oil formation and thereby allow a greater recovery of crude oil from the formation.
Another recovery technique involves the application of thermal energy in the form of the huff and puff or steam soak process to reduce the viscosity of the oil in the formation. The huff and puff or cyclic steam process is in individual well stimulation process wherein steam is injected into the formation through an injection well, stopping the injection of steam, permitting the formation to soak for a period of time and then back producing oil through the original injection well. As the heated region surrounding the steam injection well cools with time, the stimulation effect declines. As the oil viscosity increases, the well is then re-stimulated by successive steam injection and soaking cycles.
The present application has a relationship to U.S. Application Ser. No. 331,425, by W. C. Hunt, filed concurrently herewith. In Ser. No. 331,425 there is disclosed a thermal solvent method for recovering viscous crude oil from a subterranean, viscous oil-containing formation penetrated by an injection well and a spaced-apart production well. Crude oil is produced from the formation via the production well and a portion of the produced oil is subjected to a visbreaking operation to produce a crude oil having reduced viscosity. The hot visbroken produced oil is injected into the formation via the injection well as a solvent flood to reduce the viscosity of the unrecovered oil remaining in the formation and oil is produced through the production well. Also, a predetermined amount or slug of the hot visbroken produced oil may be injected into the formation via the injection well followed by another fluid such as a liquid or gaseous drive fluid to displace the visbroken produced oil solvent through the formation toward the production well from which oil is produced at an enhanced rate of recovery.
The present method is an improved cyclic thermal solvent single well stimulation method utilizing hot visbroken produced oil as the solvent injected into the formation followed by a soaking period to reduce the viscosity of the oil contained therein and enhance its recovery.